DESCRIPTION (Verbatim from the application): A prospective study of pediatric transfusion recipients will be conducted to determine the residual risk of transmitting known infectious agents such as hepatitis viruses, HIV and HTLV, for which there are current donor screening assays, and the potential risk of known agents that are not routinely screened during blood donation, but might, nonetheless, infect blood recipients with diseases such as cytomegalovirus, parvovirus B-19, human herpes virus-8 (HHV-8) and newly proposed hepatitis viruses, TTV and SEN-V. An additional primary goal of the study will be to establish a repository of linked donor and recipient samples so that if a new infectious agent emerges in the future, testing of the repository will rapidly establish whether or not that agent presents a threat to the blood supply. To insure larger numbers of samples and greater statistical power, samples from this study will be merged into a large repository to be generated in the NHLBI-sponsored RADAR (REDS Allogeneic Donor and Recipient) study. The current study will be the only pediatric arm of the RADAR multi-center study. Further, the current pediatric study will be undertaken collaboratively with a similarly designed study in adults being conducted at the NIH Clinical Center. In both studies recipients will be enrolled prior to transfusion and then followed for at least 6 months post-transfusion. Blood samples will be obtained before and at 2, 4, 8, 12, 16 and 24 weeks after transfusion. Molecular and serologic testing will be routinely performed for the agents cited above with particular emphasis on molecular assays for HRV, HCV. HIV, SEN-V, CMV, parvovirus B-i 9 and HHV-8. Aliquots will be retained in frozen storage. In addition, pre and post-transfusion and donor whole blood samples will be frozen to allow for recovery of recipient DNA and identification of microchimerism. Such microchimerism may result in transfusion-associated graft versus host disease and immunosuppression and have long term consequences for the development of immune mediated diseases in the recipient. In summary, the primary pediatric study and the proposed collaborations will allow for determinations of the transfusion risk of a variety of blood-screened and unscreened infectious agents, and will allow for comparisons of transfusion risk between pediatric and adult patients, as well as comparisons of viral persistence and clinical outcome according to age. In addition, by contributing pre and post-transfusion samples from blood recipients and their linked donor samples, this study will help establish a large serum and cell repository that will allow for the future determination of whether virtually any infectious agent is transfusion-transmitted and a potential risk to blood recipients.